1. Technical Field
The present invention relates to a method for manufacturing a liquid ejecting head which has a piezoelectric element.
2. Related Art
A piezoelectric body containing crystals represented by lead zirconate titanate (PZT) is applied to various devices such as a piezoelectric element since it has spontaneous polarization, a high-permittivity, an electro-optical effect, a piezoelectric effect, a pyroelectric effect or the like. In the case of using the piezoelectric effect, a pair of electrodes is formed at the piezoelectric body to configure a piezoelectric element, thereby applying a voltage between the electrodes, and the piezoelectric body is deformed according to the voltage. In addition, a liquid ejecting head and a liquid ejecting apparatus of an ink jet printer are known, wherein, as a part of a pressure generating chamber communicating with a nozzle opening which discharges ink as liquid is configured with a vibration plate, the vibration plate is deformed by the piezoelectric element to compress the ink in the pressure generating chamber so that the ink is discharged from the nozzle opening.
For example, since the lead zirconate titanate has a pillar shape, it may be easily destroyed due to cracks generated from the grain boundary, caused by a stress. The stress applied to the piezoelectric body includes stress caused by expansion and shrinkage of the piezoelectric body, stress caused by deformation of the vibration plate, and stress caused by the electrodes.
The stress caused by electrodes is greatly influenced by the stress formed above the piezoelectric body formed on the vibration plate, a so-called upper electrode. As a structure of the upper electrode, a two-layered structure having an intermediate film is known in the art (for example, see JP-A-2009-196329). As the intermediate film, iridium, platinum and palladium are used.
If the distance between the nozzle openings is decreased and the density is increased in order to support the increased presision in printing of recent years, the volume of the pressure generating chamber is reduced, and thus, in order to ensure the amount of ejected liquid, it is required to increase the deformation amount of the piezoelectric body so that the excluded volume is increased. In addition, accompanied by the reduced volume of the pressure generating chamber, it is required that the piezoelectric body has a small thickness.
If an electrode containing iridium, platinum and palladium is formed with a thickness of several tens of nanometers or above on the piezoelectric body by means of a sputtering method in order to improve the adhesion with the piezoelectric body, the electrode captures the sputtered gas and is elongated. As a result, compression stress is generated by the residual stress so that a tension stress may be easily applied to the piezoelectric body. If the tensile force is applied to the piezoelectric body, the pillar shaped grain boundary spreads, and thus cracks are easily created at the piezoelectric body.